The invention relates to microcavity devices and more particularly to a method and device for producing radiation useful in lithography systems.
Integrated circuits are fabricated using lithography systems with a variety of radiation sources, such as for example mid-ultraviolet lithography. These sources produce ultraviolet radiation with wavelengths in the range of 100 to 500 nanometers. The ultraviolet radiation is used to expose photoresist during integrated circuit fabrication. Radiation emissions with wavelengths of 253-254 nanometers are produced by known microdischarge lamps using a discharge gas.
A known microdischarge lamp has a substrate, a cathode plug, a dielectric layer, and an anode layer. The lamp has a microcavity etched in the shape of a cylinder. The microcavity has an open end and a closed end. The microcavity extends through the anode and dielectric layers. The microcavity extends into the cathode layer to form a microcavity base. The diameter of the microcavity is in the range of 1 to 400 microns. The microcavity acts as a container for a discharge gas of mercury or xenon iodine. The discharge gas is supplied to the microcavity under pressure. The substrate layer and anode layer are formed of conductive materials. The cathode layer is formed of a doped silicon and the dielectric layer is formed of silicon dioxide. The cathode layer is secured to the substrate layer by an epoxy layer.
By using a semiconductor material for the cathode layer, uniform voltages can be formed along the length of the microcavity. A discharge gas that is maintained in the microcavity under pressure and subjected to electric current emits radiation through the open end of the microcavity. High energy electrons are released by the discharge gas which allows access to higher energy or ion states of gaseous atoms or molecules.
It has been suggested to operate a lamp by supplying a discharge gas to a microcavity and applying a constant electrical current of 4 milliamps between the anode and substrate layers. The discharge gas is supplied to the microcavity at a pressure of up to 200 torr. The lamp emits radiation with wavelengths in the 253 to 254 nanometer range. The lamp can be used in a lithography system. Radiation emitted from the lamp may be reflected off mirrors and through masks or reticles and onto the semiconductor wafer surface.
Ideal reflective surfaces for mirrors used in lithography systems include surfaces formed from molybdenum silicon (MoSi) and molybdenum beryllium (MoBe) compounds. These compounds attain their highest reflectivities, approximately 70%, when reflecting radiation with wavelengths in the 11 to 14 nanometers range. Therefore, what is needed is a microcavity discharge device which produces radiation emissions with wavelengths of less than 253 nanometers, and more particularly wavelengths in the range of from about 11 to about 14 nanometers.
The invention relates to a microcavity device which produces radiation with wavelengths in the extreme ultraviolet region. In accordance with one embodiment, the device has a semiconductor plug, a dielectric layer, and an anode layer. The dielectric layer electrically separates the semiconductor layer from the anode layer. A microcavity with an open end is formed in the anode layer. The microcavity extends through the dielectric layer and has a base in the semiconductor plug. Optionally, a substrate layer having an aperture aligned with the microcavity can be formed on the bottom surface of the semiconductor plug.
The microcavity is filled with a pressurized discharge gas, and the anode and substrate layers are supplied with a combination of constant and pulsed currents. The electrical pulses produce radiation from the discharge gas which are emitted from the microcavity through the bottom of the semiconductor layer and the aperture of the substrate layer. The radiation can be directed as a beam onto mirrors in an optical system. The mirrors be formed with highly reflective surfaces. When the discharge gas is xenon, the radiation has wavelength peaks in the range of from about 11 to about 14 nanometers.
In accordance with another aspect of the invention, a thin metal layer is located between the semiconductor plug and the substrate layer. When the metal layer is beryllium, the emitted radiation has wavelengths between 11 and 12 nanometers (wavelengths greater than about 12 nanometers are absorbed by the beryllium layer).